Liquid crystal display device and method for manufacturing thereof

ABSTRACT

The present invention relates to a liquid crystal display that maintains a more uniform cell gap and improves adherence between two display panels by improving adhesion between substrates and their bead spacers, as well as a manufacturing method thereof. An exemplary liquid crystal display includes: a first substrate and a second substrate facing each other; a bead spacer comprising a plurality of beads and a first adhesive coupling the beads to the first substrate; a second adhesive corresponding to the bead spacer and disposed on the second substrate so as to contact the bead spacer; and a liquid crystal layer disposed between the first substrate and the second substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to, and the benefit of, Korean PatentApplication No. 10-2011-0022387 filed in the Korean IntellectualProperty Office on Mar. 14, 2011, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a liquid crystal display and amanufacturing method thereof. More particularly, the present inventionrelates to a liquid crystal display that more uniformly maintains a cellgap and improves adherence between two display panels, as well asmanufacturing methods thereof.

(b) Description of the Related Art

A liquid crystal display (hereinafter referred to as an LCD) is one ofthe most widely used types of flat panel displays. An LCD typicallyincludes two display panels provided with electric field generatingelectrodes, such as pixel electrodes and a common electrode, and aliquid crystal layer interposed between the two display panels. In theLCD, voltages are applied to the electric field generating electrodes togenerate an electric field in the liquid crystal layer. Due to thegenerated electric field, liquid crystal molecules of the liquid crystallayer are aligned, which controls polarization of incident light,thereby displaying images.

In a liquid crystal display, an upper panel and a lower panel aretypically combined by a sealant, which is disposed on an edgecircumference of the upper panel and the lower panel and which enclosesthe liquid crystal layer. Also, an interval between two display panels,that is, a cell gap, may be relatively uniformly maintained by a spacerdisposed between the upper panel and the lower panel.

Here, the spacer may be classified as bead spacers or column spacers. Ingeneral, the bead spacer has a spherical shape and is irregularlydispersed on a substrate, and the column spacer is formed to have apredetermined pattern through a photolithography process.

The bead spacer may be formed without a photolithography process, suchthat the manufacturing process is simple compared to the column spacerand its manufacturing cost is low. However, its adhesion with substratesis relatively weak, such that it is more difficult to maintain a uniformcell gap when an external force is applied to the liquid crystaldisplay.

A recent trend has seen efforts directed toward development of aflexible display device that may be flexibly bent and rolled. When theflexible display device is manufactured using bead spacers and thesubstrate is bent, the cell gap is not uniformly maintained, such that aluminance difference in a region is generated. Also, such bending maymove the bead spacer, such that an alignment layer disposed on thesubstrate may be damaged.

Further, when combining the upper panel and the lower panel by only thesealant formed at the edge circumference of the substrate, there is nomember fixing the two display panels at the center of the substrate,resulting in a weak bond between the substrates.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat.

SUMMARY OF THE INVENTION

The present invention provides a liquid crystal display that moreuniformly maintains a cell gap even when a substrate is bent, byimproving adhesion between a bead spacer and the substrate. Alsoprovided is a manufacturing method thereof.

Also described is a liquid crystal display improving adherence betweentwo display panels by using the bead spacer to fix two display panels,and a manufacturing method thereof.

A liquid crystal display according to the present invention includes: afirst substrate and a second substrate facing each other; a bead spacercomprising a plurality of beads and a first adhesive coupling the beadsto the first substrate; a second adhesive corresponding to the beadspacer and disposed on the second substrate so as to contact the beadspacer; and a liquid crystal layer disposed between the first substrateand the second substrate.

The first adhesive and the second adhesive may be made of the samematerial.

The first adhesive and the second adhesive may be a thermosettingadhesive.

The first adhesive and the second adhesive may be made of a materialthat does not react with the liquid crystal layer.

The first adhesive and the second adhesive may be made of a materialincluding an epoxy group with a content of metal ions of less than about10 ppb.

The first substrate and the second substrate may be flexible substrates.

The liquid crystal display may further comprise color filters and alight blocking member positioned between the color filters, where thebead spacer is positioned on the light blocking member.

A method for manufacturing a liquid crystal display according to thepresent invention includes: (a) forming a bead spacer on the firstsubstrate, the bead spacer comprising a plurality of beads mixed with afirst adhesive; (b) forming a second adhesive on the second substrate ata position corresponding to the bead spacer; (c) forming a liquidcrystal layer between the first substrate and the second substrate, andcombining the first substrate and the second substrate; and (d)hardening the bead spacer and the second adhesive.

In (a) and (b), the bead spacer and the second adhesive may each beformed by a printing method.

The first adhesive and the second adhesive may be made of the samematerial.

The first adhesive and the second adhesive may be a thermosettingadhesive.

The first adhesive and the second adhesive are made of a material thatmay not react with the liquid crystal layer.

The first adhesive and the second adhesive may be made of a materialincluding an epoxy group with an amount of metal ions of less than about10 ppb.

The first substrate and the second substrate may be flexible substrates.

In the above, (a) may further comprise forming the bead spacer on alight blocking member formed on the first substrate.

The liquid crystal display according to the present invention may moreuniformly maintain its liquid crystal cell gap even if the substrate isbent. This is accomplished by improving the adhesion between thesubstrate and the bead spacer. This improved adhesion may help toprevent damage to the alignment layer.

The bead spacer is used to fix two display panels such that adherencebetween the two display panels may be improved.

The spacer is formed without a photolithography process, such that themanufacturing process may be simplified and a developing solution is notused. This results in a more environmentally friendly fabricationprocess.

The bead spacer is formed by a printing method, such that the beadspacer may be formed at a regular and desired position. In detail, thebead spacer is positioned to correspond to a respective light blockingmember, so that light leakage may be reduced and aperture ratio may beincreased.

Also, the bead spacer has improved compression characteristics such thatthe drip margin of the liquid crystal may be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a liquid crystal display accordingto an exemplary embodiment of the present invention.

FIG. 2 is a view showing a bead spacer formed on the first substrate ofa liquid crystal display according to an exemplary embodiment of thepresent invention.

FIG. 3 is a view showing the second adhesive formed on the secondsubstrate of a liquid crystal display according to an exemplaryembodiment of the present invention.

FIG. 4 to FIG. 6 are cross-sectional views showing a manufacturingmethod of a liquid crystal display according to an exemplary embodimentof the present invention.

FIG. 7 and FIG. 8 are graphs showing a change of a cell gap according aliquid crystal amount in a liquid crystal display of the presentinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. As those skilled in the art will realize,the described embodiments may be modified in various different ways, allwithout departing from the spirit or scope of the present invention.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. Like reference numerals designate likeelements throughout the specification. It will be understood that whenan element such as a layer, film, region, or substrate is referred to asbeing “on” another element, it can be directly on the other element orintervening elements may also be present. In contrast, when an elementis referred to as being “directly on” another element, there are nointervening elements present.

Firstly, a liquid crystal display according to an exemplary embodimentof the present invention will be described with reference toaccompanying drawings.

FIG. 1 is a cross-sectional view of a liquid crystal display accordingto an exemplary embodiment of the present invention. FIG. 2 is a viewshowing a bead spacer disposed on the first substrate of a liquidcrystal display according to an exemplary embodiment of the presentinvention, and FIG. 3 is a view showing the second adhesive disposed onthe second substrate of a liquid crystal display according to anexemplary embodiment of the present invention.

A liquid crystal display according to an exemplary embodiment of thepresent invention includes a first substrate 110 and a second substrate210 facing each other, a bead spacer 320 disposed on the first substrate110, a second adhesive 324 disposed on the second substrate 210, and aliquid crystal layer 3 disposed between the first substrate 110 and thesecond substrate 210.

The first substrate 110 and the second substrate 210 may each be made ofa flexible material such as a plastic. When the first substrate 110 andthe second substrate 210 are made of the flexible material, they may beused in a flexible display device that may be bent or rolled. That is,“flexible” substrates 110, 210 are sufficiently flexible to allow theresulting display device to be bent or rolled.

A thin film transistor and a pixel electrode 191 connected thereto aredisposed on the first substrate 110. The thin film transistor includes agate electrode 124 disposed on the first substrate 110, a gateinsulating layer 140 disposed on the gate electrode 124, a semiconductorlayer 151 disposed on the gate insulating layer 140, a source electrode173 and a drain electrode 175 separated from each other on thesemiconductor layer 151, and a passivation layer 180 disposed on boththe source electrode 173 and the drain electrode 175 and including acontact hole exposing a portion of the drain electrode 175. The pixelelectrode 191 is connected to the drain electrode 175 through thecontact hole.

A color filter 230 is disposed on the pixel electrode 191, and a lightblocking member 220 is disposed between adjacent color filters 230. Thelight blocking member 220 is disposed to at least approximatelycorrespond to the thin film transistor.

A common electrode 270 is disposed on substantially the entire surfaceof the second substrate 210.

As shown in FIG. 2, the bead spacer 320 includes beads 320 a and a firstadhesive 320 b that are mixed and formed on the first substrate 110. Thefirst adhesive 320 b substantially encloses the beads 320 a (or at leastencompasses an area between the beads 320 a and the correspondingunderlying surface), thereby adhering the beads 320 a to the firstsubstrate 110.

The bead spacer 320 may be disposed on the light blocking member 220 ina single layer, i.e. not stacked upon one another, and/or all atsubstantially the same elevation. The bead spacer 320 is disposed tocorrespond to the light blocking member 220 such that light leakage maybe reduced and an aperture ratio may be increased as compared to thecase of bead spacers 320 that are disposed in the pixel area.

As shown in FIG. 3, the second adhesive 324 is disposed on the commonelectrode 270 of the second substrate 210. The second adhesive 324 isdisposed to correspond to the bead spacer 320, such that the bead spacer320 is adhered to the second substrate 210.

The first adhesive 320 b and the second adhesive 324 may be made of thesame material. For example, they may be made of a thermosetting adhesiveor a UV hard setting adhesive. It is preferable that the second adhesive324 is made of a thermosetting adhesive when the first adhesive 320 b ismade of a thermosetting adhesive, and that the second adhesive 324 ismade of a UV hard setting adhesive when the first adhesive 320 b is madeof a UV hard setting adhesive. In the case that the first adhesive 320 bis a thermosetting adhesive and the second adhesive 324 is made of a UVhard setting adhesive, when heat is applied to adhere the bead spacer320 to the second substrate 210, only the first adhesive 320 b isreacted, such that adhesion does not progress normally. In contrast,when UV is irradiated, only the second adhesive 324 is reacted such thatadhesion also does not progress normally. Accordingly, the firstadhesive 320 b and the second adhesive 324 may preferably be made of thesame material.

The first adhesive 320 b and the second adhesive 324 are preferablyformed of a thermosetting adhesive rather than a UV hard settingadhesive. When the bead spacer 320 is disposed to correspond to thelight blocking member 220, if the first adhesive 320 b is made of a UVhard setting adhesive, when UV light is irradiated upon the firstsubstrate 110, the UV is blocked by the light blocking member 220 suchthat UV light does not reach the first adhesive 320 b and adhesion doesnot progress in normal fashion, i.e. the adhesive does not adequatelyset. In contrast, if the first adhesive 230 b is made of a thermosettingadhesive, when heat is applied outside the first substrate 110, the heatis not influenced by the light blocking member 220 and is transmitted tothe first adhesive 320 b such that the adhesive sets and adhesionprogresses well.

The first adhesive 320 b and the second adhesive 324 may be made of amaterial that does not react with the liquid crystal layer 3. The firstadhesive 320 b and the second adhesive 324 are disposed between thefirst substrate 110 and the second substrate 210 along with the liquidcrystal layer 3 such that the first adhesive 320 b and the secondadhesive 324 may contact the liquid crystal layer 3. Thus, if the firstadhesive 320 b and the second adhesive 324 are made of a material thatreacts with the liquid crystal layer 3, the characteristics of theliquid crystal layer 3 may be altered for the worse.

Both the first adhesive 320 b and the second adhesive 324 preferably donot include metal ions, so as not to react with the liquid crystal layer3. For example, the first adhesive 320 b and the second adhesive 324 maybe made of a material of an epoxy group having an amount of metal ionsof less than about 10 ppb (parts per billion).

Next, a manufacturing method of a liquid crystal display according to anexemplary embodiment of the present invention will be described withreference to the accompanying drawings.

FIG. 4 to FIG. 6 are cross-sectional views showing a manufacturingmethod of a liquid crystal display according to an exemplary embodimentof the present invention.

First, as shown in FIG. 4, an inkjet head 410 is aligned over the firstsubstrate 110 of the flexible material, and a material of which thebeads 320 a and the first adhesive 320 b are to be made of is drippedonto the first substrate 110 through a nozzle 420 connected to theinkjet head 410, thus forming bead spacers 320.

A plurality of nozzles 420 may be formed at the lower surface of theinkjet head 410. Also, the inkjet head 410 is connected to atransferring unit (not shown) to be moved such that the material ofwhich the bead 320 a and the first adhesive 320 b are made may bedeposited in multiple regions of the first substrate 110.

A thin film transistor and a pixel electrode 191 connected thereto areformed on the first substrate 110. The thin film transistor includes agate electrode 124 formed on the first substrate 110, a gate insulatinglayer 140 formed on the gate electrode 124, a semiconductor layer 151formed on the gate insulating layer 140, a source electrode 173 and adrain electrode 175 separated from each other formed on thesemiconductor layer 151, and a passivation layer 180 formed on both thesource electrode 173 and the drain electrode 175 and including a contacthole exposing a portion of the drain electrode 175. The pixel electrode191 is connected to the drain electrode 175 through the contact hole.

A color filter 230 is formed on the pixel electrode 191, and a lightblocking member 220 is formed between adjacent color filters 230. Thelight blocking member 220 is disposed to correspond to (e.g., at leastpartially cover) the thin film transistor.

The material of which the bead 320 a and the first adhesive 320 b aremixed may be dripped to be disposed on the light blocking member 220. Bydisposing the bead spacer 320 to correspond to the light blocking member220, light leakage may be reduced and the aperture ratio may beincreased compared with the case in which the bead spacers 320 aredisposed in the pixel area.

Next, as shown in FIG. 5, the inkjet head 410 is aligned on the flexiblesecond substrate 210, and the second adhesive 324 is dripped on thesecond substrate 210 through the nozzle 420 connected to the inkjet head410.

A common electrode 270 is formed on substantially the entire surface ofthe second substrate 210, and the second adhesive 324 is formed on thecommon electrode 270 of the second substrate 210. The second adhesive324 is disposed at a position allowing contact with the bead spacer 320when combined with the first substrate 110 in a subsequent process.

Here, the second adhesive 324 is dripped in a plurality of regions onthe second substrate 210 through a plurality of nozzles 420 while movingthe inkjet head 410.

The first adhesive 320 b and the second adhesive 324 may be made of thesame material. For example, they may be made of a thermosetting adhesiveor a UV hard setting adhesive. As described above, the first adhesive320 b and the second adhesive 324 are preferably formed of thethermosetting adhesive rather than the UV hard setting adhesive.

The first adhesive 320 b and the second adhesive 324 may be made of amaterial that does not react with the liquid crystal layer (i.e., layer3 of FIG. 3). In detail, the first adhesive 320 b and the secondadhesive 324 may be made of a material from an epoxy group having anamount of metal ions less than about 10 ppb (parts per billion).

Next, as shown in FIG. 6, a liquid crystal layer 3 is formed between thefirst substrate 110 and the second substrate 210, and the firstsubstrate 110 and the second substrate 210 are combined. For example,after the liquid crystal material is dripped onto the first substrate110 or the second substrate 210, the first substrate 110 and the secondsubstrate 210 may be combined. Alternatively, after the first substrate110 and the second substrate 210 are combined, the liquid crystalmaterial may be injected between the first substrate 110 and the secondsubstrate 210.

When the first adhesive 320 b and the second adhesive 324 are made ofthe thermosetting adhesive, heat 500 is then applied outside the firstsubstrate 110 and the second substrate 210 to harden the bead spacer 320and the second adhesive 324.

The bead spacer 320 is fixed to the first substrate 110 by the firstadhesive 320 b, which has been formed to enclose the beads 320 a. Thebead spacer 320 is also fixed to the second substrate 210 by the secondadhesive 324, which has been formed at a position corresponding to thebead spacer 320.

That is, the bead spacer 320 is attached to both the first substrate 110and the second substrate 210, so that it is fixed in place. Accordingly,even if the first substrate 110 and the second substrate 210 are bent,the cell gap may be maintained substantially uniform, thus improving theadherence characteristics of the first substrate 110 and the secondsubstrate 210.

The bead spacer 320 and the second adhesive 324 are formed by aparticular printing method, being dripped onto the first substrate 110and the second substrate 210 through the nozzle 420 connected to theinkjet head 410. However, the present invention is not limited thereto,and the bead spacer 320 and the second adhesive 324 may be formed on thefirst substrate 110 and the second substrate 210 by using various othermethods.

Nanoimprint lithography, gravure printing, reverse offset printing,offset printing, and microcontact printing are examples of variouspossible printing methods.

Nanoimprint lithography is a technique for forming a minute patternthrough a precise mold of a nanoscan. In this method, a thermoplasticresin or photo-curable resin is coated on the substrate, and thenpressure is applied, similar to stamping a seal, to transcribe thepattern. Gravure printing is a printing method using a printing gravureformed by corroding the surface of a substrate to include an ink pocketmade of an anticorrosion film in the substrate by using a gravure screenand a carbon tissue for printing. In offset printing, an ink image istransferred from a printing plate to a rubber blanket, and is thenprinted. Microcontact printing is a method of forming a pattern by usingan elastic polymer stamp.

In the above-described exemplary embodiment of the present invention, acolor filter on array (COA) structure was employed in which the thinfilm transistor, the pixel electrode 191, the color filter 230, and thelight blocking member 220 are formed on the first substrate 110, and thecommon electrode 270 is formed on the second substrate 210. However, thepresent invention is not limited thereto, and various alternativestructures may instead be employed, such as a structure in which thecolor filter 230 and the light blocking member 220 are formed on thesecond substrate 210 and a structure in which the common electrode 270is formed on the first substrate 110.

Next, an effect in which a drip margin is improved in a liquid crystaldisplay will be described.

FIG. 7 and FIG. 8 are graphs showing a change in cell gap as a functionof a liquid crystal amount, in a liquid crystal display constructedaccording to an embodiment of the present invention.

In the graphs, each horizontal axis represents a liquid crystal amountthat is 100% when the liquid crystal completely fills the volumecorresponding to a space between two substrates. A number less than 100%corresponds to a situation in which the liquid crystal does notsufficiently fill the space between the two substrates, and a numbergreater than 100% corresponds to a situation in which liquid crystaloverfills the space between the two substrates.

In the graphs, each vertical axis represents an interval between the twosubstrates, that is, the cell gap.

Referring to FIG. 7, as the liquid crystal amount is increased, the cellgap is increased. When the liquid crystal amount is insufficientlyfilled at less than 100% or is excessively at filled more than 100%,deterioration may be generated. Here, it has been found that the rangeof the liquid crystal amount in which deterioration is not generated isabout more than 94% and less than 106%. Accordingly, the drip margin ofthe liquid crystal is about 12%.

In contrast, when the bead spacer is not used but the column spacer isused in the liquid crystal display of the same condition, thecorresponding range of liquid crystal amount to avoid imagedeterioration is about more than 100% and less than 106%. Accordingly,the drip margin of the liquid crystal is about 6%.

In FIG. 8, the range of the liquid crystal amount that avoids imagedeterioration due to insufficient or excessive filling of the liquidcrystal is about more than 85% and less than 107%. Accordingly, the dripmargin of the liquid crystal is about 22%.

In contrast, when the bead spacer is not used but the column spacer isused in the liquid crystal display of the same condition, thecorresponding range of liquid crystal amount to avoid imagedeterioration is about more than 100% and less than 107%. Accordingly,the drip margin of the liquid crystal is about 7%.

From the above, it can be seen that use of bead spacers instead ofcolumn spacers increases the drip margin of the liquid crystal fromabout 6% to 7% to about 12% to 22%. This is believed due to the factthat the bead spacer is made of a material having elasticity, whichresults in improved compression characteristics for the resultingdisplay.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

DESCRIPTION OF SYMBOLS

 3: liquid crystal layer 110: the first substrate 124: gate electrode140: gate insulating layer 151: semiconductor layer 173: sourceelectrode 175: drain electrode 180: passivation layer 191: pixelelectrode 210: the second substrate 220: light blocking member 230:color filter 270: common electrode 320: bead spacer 320a: beads 320b:first adhesive 324: second adhesive

1. A liquid crystal display comprising: a first substrate and a secondsubstrate facing each other; a bead spacer comprising a plurality ofbeads and a first adhesive coupling the beads to the first substrate; asecond adhesive corresponding to the bead spacer and disposed on thesecond substrate so as to contact the bead spacer; and a liquid crystallayer disposed between the first substrate and the second substrate. 2.The liquid crystal display of claim 1, wherein the first adhesive andthe second adhesive are made of the same material.
 3. The liquid crystaldisplay of claim 2, wherein the first adhesive and the second adhesiveare a thermosetting adhesive.
 4. The liquid crystal display of claim 1,wherein the first adhesive and the second adhesive are made of amaterial that does not react with the liquid crystal layer.
 5. Theliquid crystal display of claim 4, wherein the first adhesive and thesecond adhesive are made of a material including an epoxy group with acontent of metal ions of less than about 10 ppb.
 6. The liquid crystaldisplay of claim 1, wherein the first substrate and the second substrateare flexible substrates.
 7. The liquid crystal display of claim 1,further comprising color filters and a light blocking member positionedbetween the color filters, wherein the bead spacer is positioned on thelight blocking member.
 8. A method of manufacturing a liquid crystaldisplay comprising: (a) forming a bead spacer on the first substrate,the bead spacer comprising a plurality of beads mixed with a firstadhesive; (b) forming a second adhesive on the second substrate at aposition corresponding to the bead spacer; (c) forming a liquid crystallayer between the first substrate and the second substrate, andcombining the first substrate and the second substrate; and (d)hardening the bead spacer and the second adhesive.
 9. The method ofclaim 8, wherein in (a) and (b), the bead spacer and the second adhesiveare each formed by a printing method.
 10. The method of claim 8, whereinthe first adhesive and the second adhesive are made of the samematerial.
 11. The method of claim 10, wherein the first adhesive and thesecond adhesive are a thermosetting adhesive.
 12. The method of claim 8,wherein the first adhesive and the second adhesive are made of amaterial that does not react with the liquid crystal layer.
 13. Themethod of claim 12, wherein the first adhesive and the second adhesiveare made of a material including an epoxy group with an amount of metalions of less than about 10 ppb.
 14. The method of claim 8, wherein thefirst substrate and the second substrate are flexible substrates. 15.The method of claim 8, wherein (a) further comprises forming the beadspacer on a light blocking member formed on the first substrate.